1. Field of the Invention
The present invention relates to a process for decontaminating soil and waste materials. More particularly, the present invention relates to a combination of processes including a thermal combustion process, a solvent wash process that utilizes carbon dioxide generated in the thermal process, and a vaporization process that utilizes heat energy generated in the thermal process, which in combination are used to remove volatile organic compounds from soil and other waste which have various levels of contamination.
2. Description of the Related Art
For many years a major problem occurring with the development of industry, in general, and the energy and petrochemical industry, in particular, has been the need to remove the oils and other hydrocarbons that have been spilled from contaminated soil. The processes of choice have always been traditional thermal combustion processes, but the cost of these processes and the collateral damage that they can cause to the environment makes this solution unattractive in many cases. Most soil contamination is reported to be less than one percent (1%) by volume. The thermal processing of this material which contains very little hydrocarbon contamination is expensive at the very least, and most frequently causes damage to the soil. Further, the effects of the airborne contaminates and the use of ambient air in the thermal process can result in damage to a wide area.
Other treatment processes for contaminated soils lack the ability to clean or remediate the contamination. Burying soils in vaults has not been a viable or cost effective solution and the excavation and transportation of contaminated soil leaves the high possibility of scattering the pollution. The use of microorganisms or xe2x80x9cmicrobesxe2x80x9d has little value since much of the contamination either kills the organisms or they have little effect on the pollutant. Additionally, few people desire or will accept a sludge pit in their neighborhood.
It has been known to use carbon dioxide as a liquid near its critical state or as a fluid in its super-critical state to serve as an extractant for hydrocarbons from various materials. See, for example, U.S. Pat. No. 4,434,028. However, concern is now being raised over the environmental pollution resulting from emission of carbon dioxide. Carbon dioxide has been identified as one of many xe2x80x9cgreenhousexe2x80x9d gases and its increased level in the earth""s atmosphere is thought likely to contribute to an undesirable global warming effect.
It would be desirable to have a process that addresses and resolves most if not all of these concerns and interacts proactively to provide an acceptable, non-polluting, cost effective solution to this major social and environmental problem.
The present invention is a combination of parallel processes that provide optimal remediation operations for contaminated soil. Soils with high levels of heavy petroleum hydrocarbons are directed to a thermal process for destruction in a combustion process. Carbon dioxide generated and recovered in the thermal process is employed as a solvent in a solvent process to clean soils having moderate contamination with petroleum hydrocarbons and chlorinated hydrocarbon compounds. In this solvent process, contaminated soils are run through a closed soil separator where the soils are washed with carbon dioxide. The carbon dioxide is then dried from the soil and the soil is sent for segregation. Additionally, soils with the lightest forms of hydrocarbon contamination, such as gasoline, etc., are subjected to a vaporization process utilizing heat energy generated from the thermal process to heat the soil under a partial vacuum. The vapors generated are captured, condensed, and recovered as product.